You're a good officer. But these assholes are always lying. Who knows why they always fake it, but they always do.
You get to Central Booking and the woman at the gate asks if your prisoner is OK. You look in the back and see the prisoner slumped over in the seat. You immediate call for an ambulance. But it's too late.
Your prisoner is dead.
After public protests, you are criminally charged with 2nd degree depraved heart murder, misconduct in officer, second degree assault, involuntary manslaughter, manslaughter be vehicles, and reckless engagement.
Even if you get off on the charges, which seem rather harsh for an honest mistake, your career is over.